The present invention relates to hydraulic lash adjusters for internal combustion engines, and more particularly, to an improved check valve assembly for use in such lash adjusters, and to an improved method of assembling such lash adjusters.
In a conventional hydraulic lash adjuster (HLA) of the type to which the present invention relates, there is an outer body, which is typically disposed within a mating bore in the engine cylinder head, and disposed within the body is an output plunger assembly engaging a rocker arm. The output plunger assembly may be of either a one-piece or a two-piece construction, and typically, includes a ball plunger element which engages a socket formed in an “underside” surface of the rocker arm. A blind bore formed within the body cooperates with the plunger assembly to define a high pressure chamber, as is well known to those skilled in the art. There is normally a biasing spring seated within the high pressure chamber, biasing the plunger “outward” of the body bore (toward the rocker arm), as is also well known in the HLA art.
Most HLA's which are sold commercially are of the “conventional leakdown” type, in which the radial clearance space between the outer diameter of the plunger and the inner diameter of the body bore forms a leakdown path. This leakdown path (or clearance) permits communication of fluid from the high pressure chamber, through the leakdown clearance, and into the reservoir (or “low pressure” chamber) of the HLA whenever an axial force is transmitted from the rocker arm to the ball plunger.
As is well known to those skilled in the art, one of the key performance criteria of an HLA is the “leakdown” performance of the HLA, i.e., the leakdown flow and resulting plunger assembly travel, as a function of time, for a given force applied to the plunger assembly. For any given engine application, the HLA must provide a leakdown performance which is within a predetermined, specified tolerance range, in order for the HLA to be acceptable for assembly into the engine cylinder head, and in order for the engine valve gear train to operate in a manner which is satisfactory.
In a typical HLA, there is included a check valve assembly, disposed between the high pressure chamber and the low pressure (reservoir) chamber, and operable to control (either to block or to permit) fluid communication between those two chambers, in response to the instantaneous pressure differential between the chambers. Therefore, in the typical HLA, the lower end of the plunger assembly defines a check valve seat, and prior to insertion of the plunger assembly into the HLA body, the check valve assembly (typically consisting of a check ball, a spring, and some sort of retainer) is assembled to the lower end of the plunger assembly.
As is also well known to those skilled in the art, another of the key performance criteria for an HLA is the check valve assembly performance, in terms of the rate of fluid flow from the low pressure chamber into the high pressure chamber (or vice versa), in response to a particular pressure differential between the chambers. Again, for any given engine application, the HLA must provide a check valve assembly performance which is within a predetermined, specified tolerance range, in order for the HLA to be acceptable for assembly into the engine cylinder head, and in order for the engine valve gear train to operate in manner which is satisfactory.
Unfortunately, it occurs periodically that after the HLA is completely assembled, performance testing of the HLA shows that, either the leakdown performance or the check valve assembly performance is not within the specified, permissible limits. When such unacceptable performance occurs, the entire HLA is then either scrapped, (thus wasting several parts of the HLA which, individually, may have been acceptable parts, and therefore, wasting the material, labor and machining costs associated with those parts), or the HLA is sent through some sort of rework process, wherein parts are disassembled, re-inspected, re-sized, and re-assembled. Such a rework process is not only time-consuming, but is also quite expensive.
Although an HLA manufacturer normally produces several different, standard HLA models, each in relatively large volume, it is quite common for an engine manufacturer to request or need an HLA which is nearly identical to one of the standard models, but differs in respect to perhaps only one of the performance criteria, such as the leakdown performance, or the check valve performance, or the plunger travel. When the HLA manufacturer has the opportunity to make and sell such a non-standard HLA, it is then necessary for the HLA manufacturer to design (and provide tooling for) the non-standard part of the HLA, and design and test what then is effectively a whole new HLA design, and a different part number, even though the resulting HLA may have much commonality with an existing model. This approach to designing and manufacturing new HLA models adds substantially to the overall cost of manufacture of the HLA and the lead time to produce the required, non-standard HLA.